I go back to the painful subject of printing with two nozzles, it was said so many over the years that it seems worth to throw the subject, and not to remember. But yesterday, watching videos on YouTube for home-made food products, I came across the idea of using vacuum. Actually, the idea is simple in the extreme: the servo that controls the syringe with a nipple attached to the bowden tube. When using the following nozzle servo moves the plunger of the syringe, provides a reduced pressure in the bowden pipe and thereby eliminate leakage from the nozzle. Given that the flow of hot plastic is small, it can help if not get rid of the leak completely, then dramatically reduce them.
In the video, the author degas liquid silicone using similar system (but without the servo, by hands)